Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality...Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.展开更多
The orthometric height (OH) system plays a key role in geodesy, and it has broad applications in various fields and activities. Based on general relativity theory (GRT), on an arbitrary equi-geo- potential surface, th...The orthometric height (OH) system plays a key role in geodesy, and it has broad applications in various fields and activities. Based on general relativity theory (GRT), on an arbitrary equi-geo- potential surface, there does not exist the gravity frequency shift of an electromagnetic wave signal. However, between arbitrary two different equi-geopotential surfaces, there exists the gra- vity frequency shift of the signal. The relationship between the geopotential difference and the gravity frequency shift between arbitrary two points P and Q is referred to as the gravity frequency shift equation. Based on this equation, one can determine the geopotential difference as well as the OH difference between two separated points P and Q either by using electromagnetic wave signals propagated between P and Q, or by using the Global Positioning System (GPS) satellite signals received simultaneously by receivers at P and Q. Suppose an emitter at P emits a signal with frequency f towards a receiver at Q, and the received frequency of the signal at Q is , or suppose an emitter on board a flying GPS satellite emits signals with frequency f towards two receivers at P and Q on ground, and the received frequencies of the signals at P and Q are and , respectively, then, the geopoten-tial dif- ference between these two points can be determined based on the geopotential frequen- cy shift equation, using either the gravity frequency shift ? f or ? , and the corresponding OH difference is further determined based on the Bruns’ formula. Besides, using this approach a unified world height datum system might be realized, because P and Q could be chosen quite arbitrarily, e.g., they are located on two separated continents or islands.展开更多
Laser remelting(LR)has attracted widespread attention in recent years as an effective method to reduce internal defects and improve the surface quality of additively manufactured(AM)parts.In the present study,three di...Laser remelting(LR)has attracted widespread attention in recent years as an effective method to reduce internal defects and improve the surface quality of additively manufactured(AM)parts.In the present study,three different LR inter-layer scanning strategies(LR0,LR90 and LR45)and their effects on the porosity,microstructure,crystallographic texture and related mechanical properties of parts have been studied.Optical microscope,X-ray diffraction,and scanning electron microscope were used as characterization tools.In the LR90 sample,it shows obvious{111}<110>texture and strong<111>preferred orientation along the scanning direction(SD),while the 0°offset and the 45°rotation of LR scanning strategy form a finer microstructure and weak crystallographic texture.Meanwhile,the mechanical properties of the LR sample are improved compared with the sample only by laser metal deposition(LMD),and a combination of higher strength and optimal uniform elongation is obtained in the LR45 sample.The overall results show that a reasonable LR scanning strategy can reduce the anisotropy of AM parts and improve their mechanical properties.展开更多
The post-fabrication machining of additively manufactured biomedical parts is essential for achieving dimensional accuracy.However,conventional machining encounters issues in dealing with the growing demand for surfac...The post-fabrication machining of additively manufactured biomedical parts is essential for achieving dimensional accuracy.However,conventional machining encounters issues in dealing with the growing demand for surface quality and the inherent defects of parts.To improve the machining quality,the correlation between material variations and ultrasonic machining quality is investigated in terms of material properties.This variation induced by additive strategies is experimentally revealed and the mechanism for this difference is further explained through molten pool dynamic simulation.In addition,to elucidate the unique machining advantages,a hybrid cutting simulation is implemented to analyze the improving behavior of ultrasonic vibration on the common defects of additively manufactured parts.Taken together,this study demonstrates the role that material property differences play in post-fabrication machining and validates the superiority of ultrasonic machining as a post-fabrication machining method for additively manufactured parts.展开更多
基金supported by the National Natural Science Foundation of China(51975112,52375412)Fundamental Research Funds for Central Universities(N2203011)。
文摘Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.
文摘The orthometric height (OH) system plays a key role in geodesy, and it has broad applications in various fields and activities. Based on general relativity theory (GRT), on an arbitrary equi-geo- potential surface, there does not exist the gravity frequency shift of an electromagnetic wave signal. However, between arbitrary two different equi-geopotential surfaces, there exists the gra- vity frequency shift of the signal. The relationship between the geopotential difference and the gravity frequency shift between arbitrary two points P and Q is referred to as the gravity frequency shift equation. Based on this equation, one can determine the geopotential difference as well as the OH difference between two separated points P and Q either by using electromagnetic wave signals propagated between P and Q, or by using the Global Positioning System (GPS) satellite signals received simultaneously by receivers at P and Q. Suppose an emitter at P emits a signal with frequency f towards a receiver at Q, and the received frequency of the signal at Q is , or suppose an emitter on board a flying GPS satellite emits signals with frequency f towards two receivers at P and Q on ground, and the received frequencies of the signals at P and Q are and , respectively, then, the geopoten-tial dif- ference between these two points can be determined based on the geopotential frequen- cy shift equation, using either the gravity frequency shift ? f or ? , and the corresponding OH difference is further determined based on the Bruns’ formula. Besides, using this approach a unified world height datum system might be realized, because P and Q could be chosen quite arbitrarily, e.g., they are located on two separated continents or islands.
基金supported by the National Natural Science Foundation of China(No.51975112)Fundamental Research Funds for Central Universities(Nos.N180305032,N2103007)supported by the Liao Ning Revitalization Talents Program(No.XLYC1807063)。
文摘Laser remelting(LR)has attracted widespread attention in recent years as an effective method to reduce internal defects and improve the surface quality of additively manufactured(AM)parts.In the present study,three different LR inter-layer scanning strategies(LR0,LR90 and LR45)and their effects on the porosity,microstructure,crystallographic texture and related mechanical properties of parts have been studied.Optical microscope,X-ray diffraction,and scanning electron microscope were used as characterization tools.In the LR90 sample,it shows obvious{111}<110>texture and strong<111>preferred orientation along the scanning direction(SD),while the 0°offset and the 45°rotation of LR scanning strategy form a finer microstructure and weak crystallographic texture.Meanwhile,the mechanical properties of the LR sample are improved compared with the sample only by laser metal deposition(LMD),and a combination of higher strength and optimal uniform elongation is obtained in the LR45 sample.The overall results show that a reasonable LR scanning strategy can reduce the anisotropy of AM parts and improve their mechanical properties.
基金supported by the National Natural Science Foun-dation of China(Nos.51975112 and52375412)the Fundamental Research Funds for Central Universities(No.N2203003)the Singapore Ministry of Education(Grant No.A-8001225-00-00).
文摘The post-fabrication machining of additively manufactured biomedical parts is essential for achieving dimensional accuracy.However,conventional machining encounters issues in dealing with the growing demand for surface quality and the inherent defects of parts.To improve the machining quality,the correlation between material variations and ultrasonic machining quality is investigated in terms of material properties.This variation induced by additive strategies is experimentally revealed and the mechanism for this difference is further explained through molten pool dynamic simulation.In addition,to elucidate the unique machining advantages,a hybrid cutting simulation is implemented to analyze the improving behavior of ultrasonic vibration on the common defects of additively manufactured parts.Taken together,this study demonstrates the role that material property differences play in post-fabrication machining and validates the superiority of ultrasonic machining as a post-fabrication machining method for additively manufactured parts.
